A revolver is a different story as it is unsafe to have your thumbs that close to the cylinder gap.

This is a common internet half-truth I always feel compelled to comment on for balance.

While it may be true that gasses from magnum-powered ammo can injure your thumb if it's too close to the gap, it doesn't automatically mean that your thumb will be injured no matter what you're shooting. In fact, a thumbs-forward revolver grip is an option if you're shooting standard-powered (i.e. non-magnum) ammo. Many competitive revolver shooters use a thumbs-forward grip (with no adverse effects) because of the control it gives. Just remember to curl your thumb down with the hotter stuff.